1. Field of the Invention
The present invention relates to a process for fabricating coil devices to be provided in rectifier circuits, noise eliminating circuits, resonance circuits, etc., for use in various AC devices.
2. Description of the Related Art
The present applicant has proposed the process shown in FIGS. 13, (a), (b) for fabricating such coil devices (see the publication of JP-A No. 2000-277337). According to this fabrication process, a coil device as shown in FIG. 13(b) is fabricated by inserting one side portion of an air-core coil 8 into the center hole 70 of a C-shaped core 7 through a gap portion 71 thereof as shown in FIG. 13(a) and fitting the coil 8 around the core 7.
With this fabrication process, the air-core coil 8 separated from the core 7 is made, and the coil 8 is thereafter fitted around the core 7 to complete the coil device. The process is therefore simplified by eliminating the need to wind a wire around the core 7 and making the air-core coil 8 automatically.
In fabricating the above coil device, a rectangular conductor or trapezoidal conductor can be used as the conductor of the air-core coil in order to increase the ratio of the sectional area of the turns of conductor 9 passing through the center hole 70 of the core 7, to the total area of the center hole 70, i.e., the space factor of the conductor 9. When having the same cross sectional area as a round conductor, the rectangular conductor and trapezoidal conductor have a short side which is smaller than the diameter of the round conductor, so that an increased number of turns of conductor can then be accommodated in the center hole 70 of the core 7, hence a higher space factor. However, the rectangular or trapezoidal conductor has the problem of being more expensive than the round conductor.
Another process for fabricating a coil device of higher space factor is known which comprises winding a conductor 9 around a core 7 in the order indicated by the numerals of 1 to 13 in FIG. 14(a), and thereafter winding the conductor 9 around the core 7 in the order indicated by the numerals of 14 to 23 in FIG. 14(b) so as to provide one coil layer on the outer peripheral side of the core 7 and two coil layers on the inner peripheral side of the core 7. An increased number of turns of conductor can then be accommodated in the center hole 70 of the core 7 to result in a higher space factor.
The conduct 9 is nevertheless difficult to wind around the core 7 automatically and must be wound manually, which involves the problem of low production efficiency.
Accordingly, an object of the present invention is to provide a process for fabricating a coil device which process can be practiced automatically and achieves a high space factor without using a rectangular or trapezoidal conductor.